Air travel has continued to grow in popularity. At the same time, air carriers are serving an ever-growing population. However, while the population wants sufficient services, they may not want to accept consequences which attend provision of those services. To take a common example, as cities grow, suburbs and population centers expand toward the direction of what used to be a remotely located airport. At the same time, to serve the growing population, more flights might be added. Ultimately, people who have moved toward the airport experience some of the noise associated with air travel.
Increased airport noise presents problems. For example, in the late 1980s, the airport serving the city of Charlotte, N.C., added runway capacity to support additional air traffic needed to support the burgeoning community. However, nearby residents did not want to the additional noise that would result from the air traffic taking off from and landing on that new runway. Some of these residents went to court and obtained injunctive relief to prevent the runway from being used. Travelers who flew into and out of Charlotte experienced tremendous delays as a result.
Practically, there is no way to prevent population growth around an airport. Moreover, as a matter of law, it does not matter whether the airport was situated long before a population center ever emerged near the airport—citizens still have at least the right to seek legal relief if the noise amounts to the level of a “public nuisance.”
Noise concerns can be reduced if an aircraft is able to climb more steeply upon takeoff. An aircraft able to climb more steeply is able to distance itself more quickly from points on the ground. An aircraft's rate of climb is expressed as a climb gradient γ which represents a ratio of the aircraft's lift to the aircraft's drag. FIG. 1A illustrates how an improved climb gradient γ improves an aircraft's ability to climb over and away from a populated area. At an airport 100, a first aircraft 110 has a climb gradient γ′ 120 and a second aircraft 115 has a greater climb gradient γ″ 125. Because the first aircraft 110 has a lesser climb gradient γ′ 120 than the climb gradient γ″ 125 of the second aircraft 115, the first aircraft 110 cannot climb as steeply as the second aircraft 115. As a result, the first aircraft 110 with the lesser climb gradient γ′ 120 passes more closely over neighboring houses and other structures 140. Because noise is attenuated with distance, from the perspective of occupants of the houses and other structures 140, the second aircraft 115 yields less noise. Accordingly, increasing the climb gradient effectively reduces noise around an airport.
Improving the climb gradient of an aircraft not only can effectively reduce noise around airports, but can yield other benefits. To name one example, an aircraft with an improved climb gradient can carry a larger payload. The Federal Aviation Administration (FAA) mandates that an aircraft must meet a certain minimum climb gradient at take off. As a result, on hot days or at high altitude airports it is not unusual for a carrier to have to offload passengers or luggage in order to meet FAA safety guidelines to be able to depart. By decreasing drag, the denominator of the climb gradient, the climb gradient is increased. For instance, for every reduction of 0.0001 in the drag coefficient, the denominator of the climb gradient, a Model 777 commercial jetliner manufactured by The Boeing Company can carry an additional two-hundred pounds of payload. In other words, for every 0.0001 improvement in the drag coefficient, a Model 777 commercial jetliner can safely carry another average passenger. Thus, improved/reduced drag not only reduces noise around airports, but can allow carriers to operate more efficiently, thereby reducing costs.
FIG. 1B shows a conventional wing assembly 150 having a wing 160, an engine nacelle 170, and an engine nacelle mount 180 securing the engine nacelle 170 to the wing 160. The wing 160 is equipped with a leading edge high lift device 165, such as a flat panel Krueger flap, a variable camber Krueger flap, or a slat which is shown in a deployed position in FIG. 1B. A flow of fluid 190, which in this case is air, strikes a leading edge 195 of the wing assembly 150 in an operational angle of attack situation, such as takeoff, climbing, level flight, and other situations. As the flow of fluid 190 passes around the engine nacelle 170, a turbulent flow 198 results over the wing 160. Such turbulent flow 198 is understood by one ordinarily skilled in the art as occurring in the wake of fluid flow occurring after the fluid flow has passed over a body. This turbulent flow 198 causes drag over the wing 160. As previously described, drag reduces the climb gradient and, thus, results in added noise around airports.
There is an unmet need in the art for reducing noise produced by aircraft around airports. Thus, there is an unmet need for reducing drag. Reducing drag over an aircraft wing can increase the climb gradient of the aircraft, and effectively reduce the noise generated by aircraft around airports. Improved climb gradient can also enable carrying greater payloads.